<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button id="btn" >肥龙神 </button>
    <script>
    var btn=document.getElementById('btn')
    btn.addEventListener('click',fn3);
    btn.addEventListener('dblclick',fn1);
        var num=0;
    function fn3() {
        num=0;
        var hu=setTimeout(fn,1000);

    }
    function fn() {
        if (num==0) {
            alert('2班');
            clearTimeout(hu);   
        }     
        
    }
    function fn1() {
        num++;
        alert('4班');
    }
    </script>
</body>
</html>